Project Summary/Abstract Breast cancer (BC) is the most commonly diagnosed cancer and the second leading cause of cancer mortality among women in the US (ACS, 2017). High baseline prevalence, increasing screening rates, and better treatments have all contributed to a large population of BC survivors that will increase from an estimated 3.5 million in 2016 to a projected 4.5 million in the next 10 years (ACS, 2017). Multiple studies document fear of cancer recurrence (FCR) as a top long- term concern of both cancer survivors and their significant others that impacts on quality of life. Despite an increasing emphasis on FCR in the literature, a critical gap in knowledge is how FCR can produce health behavior consequences with known implications for long-term health outcomes. The overall objective of this proposal is to examine medication adherence, physical activity/sedentary behavior, and sleep as three proximal health behavior outcomes that are modifiable and have been linked to recurrence (for patients) as well as morbidity and mortality (for both patients and spouses/partners). Moreover, FCR and health behaviors are concordant within-couple reflecting an interdependent and interpersonal context that, if ignored, would limit a complete understanding of important health consequences of FCR. Preliminary data from a recently completed NCI-funded R21 project form the scientific premise and the basis of power analyses for the specific and exploratory aims. Using longitudinal, within-person methods as well as individual and dyadic multilevel structural equation modeling, we will pursue the following hypothesis-driven aims: 1) identify the consequences of FCR for physical activity; 2) identify the consequences of FCR for adherence to adjuvant hormonal treatment; and 3) identify the consequences of FCR for sleep quantity and quality. Finally, using biomarkers of cardio- metabolic health risk (i.e., HbA1c, lipids, insulin resistance, body composition), we will explore the links between the targeted health behaviors and these health outcomes. A long-term objective of the proposed work is to influence the development and refinement of interventions for FCR and health behaviors ultimately increasing optimal mental and physical well-being of cancer survivors and their spouses/partners.